Diazo development process



8 6, 1966 c. M. AEBI ETAL 3,

DIAZO DEVELOPMENT PROCESS Filed se t; 20, 1962 5 Sheets-Sheet 1 bj m G/BGZOG C) G T22 1s 24 FIG 2 INVENTORS CLAUDE M. AEBI U BRUCE E. FORSYTH AGENT g- 16, 1966 c. M. AEBI ETAL 3,266,896

DIAZO DEVELOPMENT PROCESS Fileq Sept. 20, 1962 5 Sheets-Sheet 2 BEFORE DEVELOPMENT- T|ME=0 FIG; 3

a ww w wwa/ 21 L .2 2

zzmllrzlsmzrw'i DURING DEVELOPMENT- TIME=3 SEO.

FIG. 4

DEVELOPMENT COMPLETED- TIME- 15 SEC.

E FIG. 5

Aug.16, 1966 MAEBI ETAL 3,266,896

I LOG. MEG/0.5 MIN.

DIAZO DEVELOPMENT PROCESS Filed Sept. 20, 1962 5 Sheets-Sheet;

AMMONIA GENERATION AMMONIA GENERATION FROM R AMMONIUM CARBONATE \1\W|TH0UT BARRIER GROUND LEVEL AT ROOM TEMP.

WITH SILICONE OIL BARRIER GROUND LEVEL AT Room TEMP.

alkaline or relatively alkaline conditions.

United States Patent 3,266,896 DIAZO DEVELGPMENT PRUQESS Claude M. Aebi, Endicott, and Bruce E. Forsyth, Vestal, N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York I Filed Sept. 20, 1962, Ser. No. 224,923 1 4 Claims. (Cl. 96-49) This invention relates to a diazo copy process and more particularly to an ammonia generation and control device for carrying out the process.

In diazotype printing or reproducing processes, paper or a carrier having thereon a light-sensitive diazo compound is exposed to light under a drawing or other image so as to destroy or decompose the diazo compound at the points to which the light penetrates with the portions of the paper overlaid by the .opaque areas of the drawing being protected from such decomposition. Development of the print is then effected by causing the undecomposed diazo compound on the areas overlaid by the opaque portions of the drawing to combine or couple with a coupling component or azo dyestuff component to produce a colored image corresponding to the original design.

Diazotype processes use diazo compounds which in general have the property of chemically combining with coupling components or azo dyestuff components under It is normally necessary for the production of a substantial dye formation at the areas corresponding to the image to be produced, that development he carried out in alkaline media or at least at a predetermined minimal pH corresponding to the lowest pH at which the coupling of the particular diazo compound and coupling component will take place.

The development of diazotype prints has been carried out by both semi-dry and dry processes. In one form of semi-dry process, the diazo paper exposed to light under an image is subjected to treatment with an aqueous solution containing an alkali and a coupling component. In the dry process, the paper or carrier having thereon both the diazo component and the coupling component is, after exposure, developed by subjecting the paper to an atmosphere containing ammonia vapor for a sufficient length of time to raise the pH of the paper and the moisture content sufficiently to permit dye formation. In present day copy machines use of the dry process is generally preferred. Many conventional diazo copy processes use a constant dripping of aquo-ammonia onto a heated plate for ammonia generation. The excess ammonia must be removed by a venting system which increases the size and cost of the diazo machine and reduces its portability. The prior art also teaches the dry process wherein a layer of permeable textile fabric is positioned between asolid ammonia salt and the paper to be developed and heat is applied to the salt. The textile material permits a uniform concentration of ammonia developing vapors to contact the paper. However, the above mentioned processes all possess some objectionable feature, such as, an excessive odor due to insufficient control of the obnoxious and corrosive ammonia fumes, and the relative slowness of the development.

In overcoming the above objectionable features, the present invention provides an improved dry process of the type wherein an ammonia compound is heated to generate ammonia gases for developing the exposed paper contain ing the diazo compound and coupling component. An inert material which acts as a blanket and a heat sink is positioned between the ammonia compound and the exposed side of the paper. It has been found that by using a fluid type inert material, such as silicone fluid, the inert fluid acts much as a mechanical valve and allows a large area of diazo to be developed in a short time because there are no ammonia base diffusion problems inherent to a valve arrangement. vWhen heat or infra-red energy is applied, the ammonia base is generated and bubbles up through the inert fluid to develop the superposed diazo. When the heat or. infra-red energy is removed, the ammonia base generation and bubbling ceases. The inert fluid blanket will provide a much superior control over the generated ammonia gas than the fabric type blanket used heretofore.

Accordingly, a principal object of the present invention is to provide an improved dry process for developing diazotype prints.

A further object of the present invention is to provide an improved ammonia generation and control device for use in developing diazotype prints.

A still further object of the present invention is to provide an improved diazotype developing device having ammonia generation and control means, which means includes an inert fluid which acts as a mechanical valve and as a heat sink.

A still further object of the present invention is to provide an improved diazo copying machine having an exposure chamber and a development chamber, said development chamber including ammonia generation means and novel valve means for controlling said ammonia generation means.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is an isometric view of a diazo copying machine embodying the principles of the present invention.

FIG. 2 is a side sectional view of FIG. 1 showing the' exposure chamber and development chamber of the machine.

FIG. 3 is a detail elevation view taken at any point through the development chamber assembly shown in FIG. 2 and illustrating diagrammatically the mechanism of development prior to the application of heat.

FIG. 4 is a detail elevation view similar to FIG. 3 and showing the mechanism of development during the application of heat.

FIG. 5 is a detail elevation view similar to FIGS. 3 and 4 and showing the mechanism of development after the development is completed.

FIG. 6 is a graphical indication of ammonia generation with the use of a fabric barrier compared with ammonia generation with the use of an inert fluid barrier.

7 FIG. 7 is a graphical indication of the milliequivalents of ammonia generation per 30 seconds without the use of a barrier and with the use of an inert fluid as a barrier.

Referring to FIGS. 1 and 2, 10 indicates one example of a diazo copying machine embodying the principles of the present invention. The machine comprises an outer casing 11 having a glass plate 12 arranged across the top for supporting an original sheet 13 and a diazo sheet 14 in position for an exposure cycle. Extending over the top of the glass plate is a hinged pressure plate 15 which is provided with a counter-balance spring 16.

The inside of the casing (FIG. 2) is divided into an upper or exposure chamber 17 and a lower or development chamber 18 by means of a solid plate 19. The

exposure chamber houses a plurality of light tubes 20 which provide sufficient light so that the light-sensitive diazo compound on the face of the diazo paper 14 will be decomposed or destroyed at the points to which the light is allowed to penetrate through the drawing or image sheet 13. An expose switch 21 and a timer switch 22, along with suitable circuit connections, are provided to enable the operator to run the machine through a selective timed exposure cycle.

The development chamber 18 comprises a porous support plate 23 which is preferably made out of a coarse nylon mesh or cheesecloth grid and which is used to support the diazo paper 14 which has been exposed in the exposure chamber in position to be developed. A spring biased door 24 is provided in the front of the machine for gaining access to the development chamber. Rubber sealing strips '25 are provided to prevent the escape of ammonia fumes from the development chamber when the developed sheet is pulled out. Arranged across the bottom of the development chamber is a heater 26 of the hot plate type comprising a base 27 and a heating element 28 which is connected to a suitable source of electricity by way of the timer switch 22 and a develop switch 29 to enable the machineto take a selective timed development cycle. For some applications it may be desirable to employ an infra-red heat source instead of plate 26, particularly where a rapid high intensity heat is required. Supported on the heater plate 26 is a tray or container 30 for which the porous .support plate 23 serves as a cover. Placed in the con- .tainer 30 is a supply of finely pulverized ammonium carbonate 31 ((NH CO and an inert fluid 32, such as silicone oil or parafiin oil.

In operation of the machine, the drawing or original sheet 13 and the superposed diazo copy sheet 14 are placed face down on the glass plate 12, as shown in .FIG. 2, so that the image side of the original sheet contacts the glass plate and the diazo coated side of the .copy sheet contacts the back of the original sheet. The hinged pressure plate 15 is closed, the timer switch 22 is set and the expose switch 21 is depressed to turn on the light tubes 20 and start the exposure cycle. After exposure, the sheets are removed, the access door 24 is opened and the copy paper 14 is positioned on the support grid 23 with its exposed side down. The access door is then closed, the timer switch set and the develop switch depressed to turn on the heater 26 and start the development cycle. After completion of the development cycle, the diazo copy sheet is pulled out from between the rubber sealing strips 25 and removed from the development chamber.

As was previously mentioned, a feature of the present invention is the use of an inert fluid to provide superior control over the ammonia gas generated in the development chamber during the development cycle when the ammonia carbonate is being heated. FIGURES 3, 4 and V show diagrammatically the action that takes place. As

indicated in FIG. 3, before heat is applied to initiate a development cycle what ever ammonia gas is generated .at room temperature is substantially blocked from the atmosphere and from the diazo coated paper 14 by virtue of the blanket of inert fluid 32 through which the unheated ammonia gas is unable to penetrate.

Upon the initiation of a development cycle wherein the heater 26 creates a temperature which is suflicient to decompose the ammonia salt in the pulverized ammonium carbonate 31, the action'thereof will be equivalent to that illustrated diagrammatically in FIG. 4. Each particle of the ammonia salt, upon being brought to the temperature suflicient to cause its decomposition,

immediately liberates ammonia gas which bubbles up through the inert fluid blanket or barrier 32. The ammonia gas bubbles, indicated as 31a will seep through the porous grid support 23 to develop the superposed .diazo coated paper 14. And, similar to the action of bubbles in a boiling liquid, the bubbles of ammonia gas 31a will propagate themselves in alldirections so that the diazo paper will be subjected uniformly to the liberated gas.

At the end of the development cycle when the heat is turned off, as indicated in FIG. 5, the ammonia base generation ceases and the bubbling of ammonia gas stops 4 immediately. The inert fluid acts as a heat sink to aid in temperature dissipation and also, there will be practically no escape of any lingering gas fumes due to the resistance afforded by the inert liquid blanket. When the operating temperature is dropped sufliciently, the force required to disperse any gas bubbles through the inert liquid is no longer present and it can be seen that the inert fluid material acts much as a mechanical valve, but allows a large area of diazo to be developed in a short time because there are no ammonia base diffusion problems inherent to a valve arrangement.

A preferred form of inert fluid which has been found to function extremely well in this respect is silicone oil. Silicone as used in the trade is a generic term for a line of heat-stable, organo-silicon oxide polymers made by combining silicon dioxide with methyl or ethyl groups stability, inertness waterproofness, and excellent dielectric properties. Although silicone fluid is especially desirable because it retains its uniform viscosity over a wide range of temperatures, other inert fluids such as parafiin oil could be used. In fact, any petroleum fraction or any non-reactive liquid which has a viscosity above centipoises could be employed as a blanket or barrier for the ammonia gas.

A very desirable feature of the present arrangement is considered to be the rapid rate of stoppage of ammonia generation to the atmosphere after the heat is removed. 'FIG. 6 is thought to show a general comparison of the ammonia generation characteristics when an inert fluid blanket or barrier is used and when a porous fabric barrier is used. The rate of turned-off of ammonia generation to the atmosphere is considered to be substantially slower when a fabric barrier is used due to the fact that even at room temperature ammonia gas is allowed to escape through the pores of the fabric to create an excessive odor and also a substantial amount of ammonia is absorbed on'the fabric, whereas the inert fluid provides a much more positive barrier to prevent the escape of gas after the heat is removed. The rate of turn-on will be substantially the same in either case.

Referring to FIG. 7, there is shown a comparison of the characteristic curves of ammonia generation without the use of a barrier and with the use of a silicone oil barrier. The logarithmic value of milli-equivalents of ammonia generation per 30 seconds is shown plotted against time using the known standards of measurement wherein 17 grams of ammonia occupies 22.4 liters and 22.4 liters at standard temperature and pressure equals 1 equivalent of gas. In arriving at the characteristic curves shown in FIG. 7, a 1 cm. layer of silicone oil (Dow Corning 200Viscosity Grade200 cstks. at 25 degrees C.) was used as a barrier layer over 10.0 grams of finely pulverized ammonium carbonate which was placed in an enclosed aluminum container and spread over an area of 4.8 square inches. An adequate flow of helium gas was passed over the surface of the ammonia carbonate to carry the generated ammonia gas into a solution of 0.2 N. hydrochloric acid where the amount of ammonia generation was measured by well-known techniques. The ammonia was generated at a rapid rate by placing the aluminum container on a 350 degree C. hot

plate. Cooling was accomplished at room temperature by 3 meq.) than it would be if no barrier was used. As heat is applied and the temperature increased, the rate of ammonia gas released is substantially the same. However, when the heat is removed and the temperature decreased it can be seen that the rate of decrease in the release of gas when the silicone oil barrier is used is much more linear and rapid than if no barrier is used. It follows that the same type of characteristics will apply if porous type barriers are used, which, although more effective than no barrier at all, would be less effective than an inert fluid barrier.

It may be pointed out that the ammonium carbonate could be used just as well in a bar or cake form rather than in powder form. There are machine applications where the sheets may be preferably handled or fed in a vertical plane, for example, and where it may be more feasible to immerse an upright bar or cake of ammonium carbonate in silicone oil.

Whilethe invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method for developing diazotype prints by ammonia gas which comprises:

arranging a diazotypeprinting carrier in the vicinity of an inert fluid having immersed therein a decomposable ammonia compound; said inert fluid being non-reactive with said ammonia compound and having a viscosity of over 100 centipoises to provide a control barrier for ammonia gas; and

heating the assembly at an elevated temperature for a predetermined length of time to cause liberated ammonia to bubble through the inert fluid to rapidly develop the print. I 2. A method for developing diazotype prints by ammonia gas which comprises:

arranging a diazotype printing carrier in the vicinity of a silicone fluid having immersed therein a decomposable compound of ammonium carbonate; said silicone fluid being non-reactive with said ammonium carbonate and having a viscosity of over 100 centipoises to provide a control barrier for ammonia gas; and

heating the assembly at an elevated temperature for a predetermined length of time to cause liberated ammonia gas to bubble through the silicone fluid to rapidly develop the print.

3. A method for developing diazotype prints by ammonia gas which comprises:

arranging a diazotype printing carrier in the vicinity of an inert fluid having immersed therein a de composable ammonia compound; said inert fluid being non-reactive with said ammonia compound and having a viscosity of over 100 centipoises to provide a means for controlling the release of ammonia gas;

heating said ammonia compound at an elevated temperature whereby ammonia gas is generated and caused to bubble through the inert fluid to contact and rapidly develop the print; and

dropping said elevated temperature after a predetermined time whereby said inert fluid will act as a valve to rapidly stop the further release of generated ammonia gas.

4. A method for developing diazotype prints by ammonia gas which comprises:

arranging a diazotype printing carrier in the vicinity of an inert fluid having immersed therein a decomposable ammonia compound; said inert fluid 'being non-reactive with said ammonia compound and having a viscosity of over 100 centipoises to provide a means for controlling the release of ammonia gas; and

heating the assembly at an elevated temperature for a predetermined period of time whereby ammonia gas is generated and caused to bubble through the inert fluid to contact and rapidly develop the print;

said inert fluid functioning as a control valve to control the rate of release of ammonia gas before, during and after said predetermined period of heat- References Cited by the Examiner UNITED STATES PATENTS 2,590,899 4/ 1952 Snelling 96-49 X 2,692,827 10/ 1954 Brinnick et al. 9633 2,773,779 12/1956 Brinnick et a1. 9649 X 2,817,279 12/1957 Ellsworth et al. 73 2,923,625 2/ 1960 Herrick 9649 2,979,404 4/1961 Ellsworth et al. 9649 FOREIGN PATENTS 562,828 7/ 1944 Great Britain.

NORMAN G. TORCHIN, Primary Examiner. R. L. STONE, A. D. RICCI, Assistant Examiners. 

1. A METHOD FOR DEVELOPING DIAZOTYPE PRINTS BY AMMONIA GAS WHICH COMPRISES: ARRANGING A DIAZOTYPE PRINTING CARRIER IN THE VINCINITY OF AN INERT FLUID HAVING IMMERSED THEREIN A DECOMPOSABLE AMMONIA COMPOUND; SAID INERT FLUID BEING NON-REACTIVE WITH SAID AMMONIA COMPOUND AND HAVING A VISCOSITY OF OVER 100 CENTIPOISES TO PROVIDE A CONTROL BARRIER FOR AMMONIA GAS; AND HEATING THE ASSEMBLY AT AN ELEVATED TEMPERATURE FOR A PREDETERMINED LENGTH OF TIME TO CAUSE LIBERATED 